1. Field of the Invention
The present invention relates to a lenticular lens sheet for light-transmissive screens to be used in rear projection televisions, etc., and to a method for product it.
2. Description of the Related Art
A light transmissive screen to be used in rear projection televisions and others generally has a constitution of two lens sheets combined. Specifically, it comprises a Fresnel lens sheet and a lenticular lens sheet as so aligned that the former is to be on the side of a light source while the latter to be on the side of a viewer, in which the Fresnel lens sheet has the function of focusing rays of image light from CRT or those having passed through a liquid-crystal system thereby to make them fall within a range of predetermined angles and the lenticular lens sheet has the function of again diffusing the rays of image light having passed through the Fresnel lens sheet thereby to make them fall within a range of suitably broadened angles.
FIG. 12 shows a fragmentary perspective view of a conventional lenticular lens sheet. As in FIG. 12, the lenticular lens sheet 11 has lenticular lenses 12 formed on its one surface that receives rays of image light incident thereon. The other surface of the lenticular lens sheet 11 through which the rays of image light having entered the sheet 11 go out is generally so formed that it has thereon a light-condensing region 13 that collects the rays of image light from the lenticular lenses 12. The light-condensing region 13 is lenticulated, as illustrated, so as to improve its capabilities to diffuse the rays of image light having entered the lenticular lens sheet 11 in the horizontal direction of the sheet 11. Especially in lenticular lens sheets of that type to be combined with three-tube CRT projectors, the light-condensing region 13 must be indispensably lenticulated so that it could have the ability to correct the color shift of three colors. In the lenticular lens sheet 11 illustrated, the non-light-condensing region 14 (except the light-condensing region 13) in which the rays of image light from the lenticular lenses 12 formed on the surface of the sheet 11 that receives the rays of image light are not condensed shall be ridged in plural ridges each having a top parallel to the sheet 11. Each top of the ridges and the sides of each ridge adjacent to its top (the upper sides thereof) are all coated with an external light-absorbing layer 15 of a black pigment or the like through roll coating, screen printing, transfer printing or the like. In that manner, the non-light-condensing region 14 shall be in the form of external light-absorbing ridges 16. With the ridges 16, the lenticular lens sheet 11 reduces a part of the external light having entered it and going out through its light exit surface toward a viewer, thereby increasing the contrast of the image which the viewer receives via the sheet 11.
However, merely coating the top and the upper sides of each external light-absorbing ridge of the lenticular lens sheet with such an external light-absorbing layer is not satisfactory for obtaining high image contrasts in surroundings where external light exists. In that condition, one subject matter of the lenticular lens sheet is to much more reduce the external light reflection on the sheet.
A method has been proposed, which comprises coating not only the top and the upper sides of each external light-absorbing ridge of a lenticular lens sheet but also the entire sides thereof with an external light-absorbing layer (see JP-A 59-87042U). According to that method, the external light-absorbing area of the lenticular lens sheet is broadened and the proportion of external light to be absorbed by the sheet is thereby increased. In ordinary lenticular lens sheets, however, the top of each lenticule constituting the light-condensing region is naturally higher than the bottom edges of each ridge constituting the external light-absorbing region. In those, therefore, even if not only the top but also the entire sides of each ridge constituting the external light-absorbing are desired to be coated with a material of forming an external light-absorbing layer through ordinary roll coating, screen printing, transfer printing or the like, it is extremely difficult to apply the light-absorbing material only onto the entire surface of the external light-absorbing region inclusive of the bottom edges of each ridge constituting the region, but not onto the lenticular lenses that constitutes the light-condensing region. In fact, in practical processes, it is difficult to produce lenticular lens sheets where the sides of all ridges constituting the external light-absorbing region are entirely coated with a material of forming an external light-absorbing layer.
The present invention has been made in consideration of the situation as above, and its object is to provide a lenticular lens sheet capable of significantly reducing external light reflection thereon and capable of giving high-contrast sharp images therethrough, and to provide a method of producing the lenticular lens sheet in a simplified manner.
To attain the object as above, the lenticular lens sheet of the invention has a plurality of lenticular lenses formed on one surface of a light-transmissive substrate, while having, on the other surface of the substrate, a plurality of convex lenses located at or near a focal position of each lenticular lens, and external light-absorbing, ridges as formed alternately with those convex lenses and coated with an external light-absorbing layer on their tops, and is characterized in that every furrow between each convex lens and each external light-absorbing ridge that are adjacent to each other is further coated with an external light-absorbing layer. In the sheet, the external light-absorbing layer to cover each external light-absorbing ridge may be not only on the top of each ridge but also around a part of each ridge adjacent to the top thereof.
The lenticular lens sheet of the invention may be produced in a method comprising applying an external light-absorbing material to a light-transmissive substrate having a plurality of lenticular lenses formed on one surface and having, on the other surface, a plurality of convex lenses located at or near a focal position of each lenticular lens, along with external light-absorbing ridges as formed alternately with those convex lenses so as to be coated with an external light-absorbing layer on their tops, thereby filling every furrow space between each convex lens and each external light-absorbing ridge that are adjacent to each other with the external light-absorbing material as applied thereto, then removing the excess external light-absorbing material existing in the area except every furrow between each convex lens and each external light-absorbing ridge that are adjacent to each other, thereby forming a layer of the external light-absorbing material only in that every furrow, and thereafter forming an additional external light-absorbing layer on each top of every external light-absorbing ridge. In the step of the method for filling every furrow space between each convex lens and each external light-absorbing ridge that are adjacent to each other, with the external light-absorbing material, the external light-absorbing material may be applied to the entire surface of the light-transmissive substrate having the convex lenses and the external light-absorbing ridges alternately thereon. In the step of the method for forming the additional external light-absorbing layer on each top of every external light-absorbing ridge, the external light-absorbing layer may also be formed around a part of each external light-absorbing ridge adjacent to the top thereof.
The lenticular lens sheet of the invention may be produced in another method comprising applying an external light-absorbing material to a light-transmissive substrate having a plurality of lenticular lenses formed on one surface and having, on the other surface, a plurality of convex lenses located at or near a focal position of each lenticular lens, along with external light-absorbing ridges as formed alternately with those convex lenses, thereby forming a first external light-absorbing layer on each top of those external light-absorbing ridges, then (1) applying a layer of an external light-absorbing material onto the entire surface of the substrate having thereon those external light-absorbing ridges, or (2) filling every furrow space between each convex lens and each external light-absorbing ridge that are adjacent to each other with an external light-absorbing material as applied thereto, and thereafter removing the excess external light-absorbing material existing in the area except every furrow between each convex lens and each external light-absorbing ridge that are adjacent to each other, thereby forming a second external light-absorbing layer only in that every furrow. Like in that of the former method mentioned previously, also in the step of this method for forming the first external light-absorbing layer on each top of every external light-absorbing ridge, the external light-absorbing layer may also be formed around a part of each external light-absorbing ridge adjacent to the top thereof.